The purpose of livestock under austere conditions is to expand the resource-net that humans can cast.
That is different than modern, "efficient" animal husbandry.
Modern husbandry often involves feeding livestock human-quality food to maximize rates of weight gain, egg production or milk production. That results in animal husbandry being a net protein and energy sink...less protein and calories are available for humans.
Consider a pig, an animal much like humans in its food needs. A 240 pound hog (pigs become hogs when they pass 180 pounds of weight) can easily eat as much as four people. If human-quality food is limited, than fattening that one hog deprives (starves) four humans. That is part of what makes the Biblical story of the Prodigal Son so haunting. The prodigal son is feeding hogs human-quality food while he, himself is starving.
There are some ecosystems where hogs make sense. An environment that produces large amounts of acorns, for instance. It is not particularly energy efficient for humans to gather acorns especially when there are other agricultural tasks competing for their time. However, it often makes sense let hogs free-range and fatten on acorns. The key is to time the growth-curve for the majority of the hogs hit peak food consumption so it coincides with acorn drop.
In general, animals that produce milk or eggs are more efficient converters of protein supplying the eggs/milk than slaughtered to supply meat.
Cows are ruminants. They have enormous stomachs (four of them!) that ferment cellulose (which humans cannot digest) into short-fatty acids that provide energy. They can eat non-human quality food and turn it into delicious food that is very dense in the nutrients needed by hard-working humans, that is, protein and fat.
Consider raising cattle for meat.
Let us say, for instance, that you have a mama beef cow. You have an accommodating neighbor who supplies the services of a bull so you don't have to feed one.
Under austere conditions, you are not feeding grain and you decide to go "seasonal" to maximize the availability of grass.
Your cow drops one calf on March 15 of every year and you slaughter that calf on November 15 of the following year as a 1350 steer or 1000 pound cow.
The hanging-weight will be about 700 pounds and the lean, boned meat will be about 550 pounds or about a pound-and-a-half of beef per day assuming you have enough power to run a freezer and can meter it out over the following year. That assumes you will eat the liver, heart and tongue. 550lbs of beef is about 140 pounds of protein.
But what did it take to make that happen? You had to overwinter 1600 pounds of beef-on-the-hoof. You had to have enough hay or stockpiled pasture to provide 4% of body weight of feed a day. That is a very honest bale-and-a-half of small square bales of hay a day or three, 800lb round bales a month.
Another consideration is that you had a 1100 pound mama cow, a 1200lb 18 month old calf and a 500lb 8 month calf grazing on November 1. That is 2800 pounds of cattle on pasture and that really cuts into your ability to "stockpile" pasture.
In 2010, New Zealand averaged 250 pounds* of milk protein per cow and they do it all on pasture. As a secondary data point, a typical American Holstein that is fed large
amounts of human-quality food produces about 750 pounds of protein per
For the most part, the New Zealand milk was produced by Jerseys, a smaller (900 pounds) dairy-breed well suited for production of milk on pasture. It should also be noted that New Zealand is blessed with an extremely clement climate and absolutely world-class farmers. The American Holstein weighs about 1400 pounds.
Suppose for the moment that our austere farmer is milking a cow that is 3/4 Holstein and 1/4 any beef breed. In general, beef breeds are better at foraging and the genetic diversity adds hybrid vigor. That is, the cows won't die if you look at them cross-eyed.
Your milk cow might weigh 1200 pounds and produce 60% of what a New Zealand cow produces in a year. I am trying to be realistic and not paint pie-in-the-sky fantasies. You might do much, much better than the 60% number.
Your cow produced 150 pounds of protein (pretty much a wash for the meat cow) and 180 pounds of butterfat and she ate 3/4 as much hay/stockpile through the winter as the beef cow and calf.
And with your milch cow, you have a much greater ability to "stockpile" pasture. Instead of having 2500 pounds of cattle grazing the pasture in September and October, you only have 1200lbs so the grass can take advantage of the autumn rains and get ahead of the animal's consumption.
Stockpiling is where you don't cut-and-dry the grass into hay. You leave it standing and let the cows harvest it.
An additional consideration is that your milk cow will produce milk from mid-March until mid-October. That is seven months of protein that does not rely on refrigeration. And, if you make cheese, it converts to a form that is available for the rest of the year.
Beef or milk?
Milk production should be the default under austere conditions because it produces the same amount of protein per mama cow on less forage-per-year than beef production. Milk production is also less sensitive to lack of refrigeration especially when paired with cheese production or fermented milk products like yogurt or viili.
It is not a total slam-dunk. Milk is more labor intensive and does not tolerate "vacations".
If conditions are exceptionally dry and forage is scarce, then beef adapts better to "extensive" agriculture.
*Milk solids are approximately 30% protein, 30% fat and 40% lactose.